The operations in volatile Helmand province could be a change in tactics in advance of an expected U.S. Marine offensive. Western forces are struggling to damp the threat of roadside bombs.

Reporting from Kabul, Afghanistan — Aerial drones fired missiles that killed 16 insurgents in separate strikes in volatile southern Afghanistan, Western military officials said Tuesday. The attacks, coming in advance of an expected offensive by U.S. Marines in the area, signaled what could be a change of tactics against Taliban fighters planting roadside bombs or laying ambushes.

Drones have been extensively used by the U.S. to attack suspected militant leaders in Pakistan's tribal areas. In the Afghan conflict, however, they have been mainly employed for surveillance purposes and used only occasionally for "pinpoint" strikes against known Taliban commanders.

In Pakistan, the relentless campaign of drone strikes, mainly carried out by the CIA, has prompted furious protests against what Pakistani authorities say have been hundreds of ancillary civilian deaths. The CIA employees killed Dec. 30 in a suicide bombing at a base in eastern Afghanistan had helped plan and coordinate such strikes.

With an allied troop buildup imminent in Afghanistan, the Western military has been struggling to quell the threat of roadside bombs. The explosive devices account for most troop fatalities and injuries, and were a major factor in the doubling of the U.S. military death toll in Afghanistan last year.

The roadside bomb toll has been especially punishing in the south, where most of the 30,000 American reinforcements set to arrive this year will be deployed.

In strikes that occurred hours apart Monday, a drone fired a Hellfire missile after a group of men was monitored moving ammunition near a suspected Taliban safe house in Helmand province's Now Zad district, the Western military said. Thirteen insurgents were killed, the North Atlantic Treaty Organization's International Security Assistance Force said in a statement.

A similar strike took place in the Nad Ali district of Helmand, where three insurgents were killed by a Hellfire missile after they "took up previously used firing positions."

"We're using everything we've got" to combat roadside bomb emplacement, said U.S. Army Col. Wayne Shanks, an ISAF spokesman, although he declined to characterize Monday's drone attacks as linked to the planned troop buildup or the expected Marine offensive.

The Marines, who seized a large swath of the Helmand River Valley over the summer, have signaled their intent to launch another offensive targeting the town of Marja, a significant narcotics-trafficking hub where many insurgents have taken shelter from fighting elsewhere in the province.

Despite concerted American efforts in recent months to build trust in dealings with local authorities in Helmand, many villagers remain deeply suspicious of foreign forces. That makes it much harder for troops to gather intelligence from locals about insurgent activities, including the planting of roadside bombs.

In Helmand's Garmsir district, villagers rioted Tuesday over allegations that Western troops had desecrated a Koran, the Muslim holy book, in an earlier raid. The confrontation turned lethal when shots were fired at a coalition base, striking an Afghan official, and Western forces fired back, killing a man they said was the shooter.

Daoud Ahmadi, a spokesman for Helmand's governor, said local reports indicated six civilians had been killed but the incident was being investigated. Military officials said the only death was that of the alleged sniper.

U.S. forces also denied that any desecration had taken place during a raid a day earlier, conducted jointly with Afghan forces and targeting the Taliban. American officials accuse the Taliban of spreading rumors about foreign troops' mishandling of the Koran -- a highly sensitive subject in religiously conservative areas such as Helmand -- to incite unrest.

"While denying these allegations, we take them very seriously and support a combined investigation with local Afghan authorities," U.S. Marine Maj. Gen. Michael Regner, ISAF's deputy chief of staff for operations, said in a statement.

In the capital, Kabul, meanwhile, American officials who oversee the spending of billions of dollars in reconstruction aid told journalists that more than three dozen cases involving graft and malfeasance were under criminal investigation.

Raymond DiNunzio of the Office of the Special Inspector General for Afghanistan Reconstruction said at a news conference that more than two-thirds of the 38 cases involved non-Afghans.

Afghan President Hamid Karzai, under intense pressure to clean up corruption in his government, often responds to international demands for reforms by alleging that Western aid efforts are honeycombed with corruption as well.

The American disclosures appeared aimed at assuring Karzai and the Afghan public that wrongdoing on the international side was not being ignored.

Corruption affecting the disbursement of aid money is expected to be a topic at a conference in London at the end of the month on reconstruction and security in Afghanistan.